linux-kernel - Re: [PATCH] perf symbols/KCORE: Rebuild rbtree when adjusting symbols for kcore

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Date:	Fri, 6 Nov 2015 22:31:05 +0800
From:	pi3orama <pi3orama@....com>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Wang Nan <wangnan0@...wei.com>, namhyung@...nel.org,
	lizefan@...wei.com, linux-kernel@...r.kernel.org, jolsa@...nel.org,
	masami.hiramatsu.pt@...achi.com
Subject: Re: [PATCH] perf symbols/KCORE: Rebuild rbtree when adjusting symbols for kcore



发自我的 iPhone

> 在 2015年11月6日，下午9:59，Adrian Hunter <adrian.hunter@...el.com> 写道：
> 
>> On 06/11/15 15:19, Arnaldo Carvalho de Melo wrote:
>> Em Fri, Nov 06, 2015 at 09:46:12AM +0000, Wang Nan escreveu:
>>> In dso__split_kallsyms_for_kcore(), current code adjusts symbol's
>>> address but only reinsert it into rbtree if the symbol belongs to
>>> another map. However, the expression for adjusting symbol (pos->start -=
>>> curr_map->start - curr_map->pgoff) can change the relative order between
>>> two symbols (even if the affected symbols are in different maps, in
>>> kcore case they are possible to share one same dso), which damages the
>>> rbtree.
>> 
>> Right, some code does change the symbol values it gets from whatever
>> symtab (kallsyms, ELF, JIT maps, etc) when it should instead use the per
>> map data structure (struct map) and its ->{map,unmap}_ip, ->pgoff,
>> ->reloc, members for that :-\
>> 
>> I.e. 'struct dso' should be just what comes from the symtab, while
>> 'struct map' should be about where that DSO is in memory.
>> 
>> With that in mind, do you still think your fix is the correct one?
>> 
>> Adrian?
> 
> The problem is when the order in memory (in kallsyms) is different
> to the order on the dso (kcore).
> 
> I think to make it more general it needs to insert to a new tree.
> e.g.
> 

Thanks to your quick reply, but I have left my office and won't have time and
environment to test your patch until next Wednesday. Is it possible for you to
test it for yourself?

Thank you.

> 
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index b4cc7662677e..09343a880c0b 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -654,19 +654,24 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
>    struct map_groups *kmaps = map__kmaps(map);
>    struct map *curr_map;
>    struct symbol *pos;
> -    int count = 0, moved = 0;
> +    int count = 0;
> +    struct rb_root old_root = dso->symbols[map->type];
>    struct rb_root *root = &dso->symbols[map->type];
>    struct rb_node *next = rb_first(root);
> 
>    if (!kmaps)
>        return -1;
> 
> +    *root = RB_ROOT;
> +
>    while (next) {
>        char *module;
> 
>        pos = rb_entry(next, struct symbol, rb_node);
>        next = rb_next(&pos->rb_node);
> 
> +        rb_erase_init(&pos->rb_node, &old_root);
> +
>        module = strchr(pos->name, '\t');
>        if (module)
>            *module = '\0';
> @@ -674,28 +679,21 @@ static int dso__split_kallsyms_for_kcore(struct dso *dso, struct map *map,
>        curr_map = map_groups__find(kmaps, map->type, pos->start);
> 
>        if (!curr_map || (filter && filter(curr_map, pos))) {
> -            rb_erase_init(&pos->rb_node, root);
>            symbol__delete(pos);
> -        } else {
> -            pos->start -= curr_map->start - curr_map->pgoff;
> -            if (pos->end)
> -                pos->end -= curr_map->start - curr_map->pgoff;
> -            if (curr_map->dso != map->dso) {
> -                rb_erase_init(&pos->rb_node, root);
> -                symbols__insert(
> -                    &curr_map->dso->symbols[curr_map->type],
> -                    pos);
> -                ++moved;
> -            } else {
> -                ++count;
> -            }
> +            continue;
>        }
> +
> +        pos->start -= curr_map->start - curr_map->pgoff;
> +        if (pos->end)
> +            pos->end -= curr_map->start - curr_map->pgoff;
> +        symbols__insert(&curr_map->dso->symbols[curr_map->type], pos);
> +        ++count;
>    }
> 
>    /* Symbols have been adjusted */
>    dso->adjust_symbols = 1;
> 
> -    return count + moved;
> +    return count;
> }
> 
> /*
> 

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